I assume LEDs will be allowed, cause they are very energy efficient (but expensive).

Prefer to get xenon fixtures for undercabinet kitchen lighting, but hate to have them be obsolete in a few years. Although the bulbs will last a very long time....and I could order extra bulbs to stockpile.

I like the option of low/high settings I can do with xenon but cannot with fluorescent--why not just automatically getting fluorescent.

(It's a retrofit situation; with backsplash already tiled and electrician says he can't put a dimmer on them, cause just going to turn them on at the lights themselves--no wall switches).

Short answer to your question if xenons be allowed after 2012, yes. I like the use of xenons as a better option to halogens as well and don't believe you'll have the risk of them going obsolete in a few years. FWIW, I'm planning to do the same with xenons for their "clean" light output and are lower heat producing compared to halogens.

I don't want to bog down the post with the content of the '07 energy act that can be referenced, but in short summary it's as follows.
The law addresses more than just light bulbs, but since ~1/5th of the energy consumption is attributed to lighting (according to the Dept. of Energy), then light bulb efficiency is an important aspect. The use of replacement flourescents is a relatively easy conversion for energy savings. The caveat I have with that conversion is your just trading towards another potential environmental concern, since flourescents contain mercury. Sure there's recycling programs as other biohazards have, but unfortunately there's folks who don't adhere to those rules for the sake of convenience.

The key points relating to light bulbs;

Requires roughly 25 percent greater efficiency for light bulbs, phased in from 2012 through 2014. This effectively bans the sale of most current incandescent light bulbs. All light bulbs must use 25% to 30% less energy than today's products by 2012 to 2014. The phase-in will start with 100-watt bulbs in January 2012 and end with 40-watt bulbs in January 2014. By 2020, bulbs must be 70% more efficient.

Various specialty bulbs, including appliance bulbs, colored lights, and 3-way bulbs, are exempt from these requirements.